In general a processing of semiconductor wafers is carried out by transferring semiconductor wafers into a plurality of processing vessels (chambers) prepared in a processing device by a transfer mechanism. For such processing of semiconductor wafers there are a sequential processing and a parallel processing. The sequential processing is performed by using a plurality of processing vessels each for executing different process, wherein a semiconductor wafer is sequentially transferred through the processing vessels. On the other hand, the parallel processing is performed by using a plurality of processing vessels for carrying out an identical process (e.g., a film formation process) and a transfer mechanism used therefor in common, wherein semiconductor wafers are sequentially transferred to the respective processing vessels by the transfer mechanism and the identical process is performed on respective wafers therein. The different processes in the sequential processing may include separate processes, e.g., a film formation process and an etching process, or a film formation process for forming films with different elements, e.g., Ti, TiN, W, WSi or the like, even in a single film formation process.
In both processing methods, temperature, pressure and other parameters in each processing vessel are controlled to be in a condition appropriate for adequately processing the semiconductor wafers, prior to loading the semiconductor wafers into the processing vessels. Hereinafter, controlling conditions of each processing vessel before performing a process will be referred to as conditioning. Such conditioning includes, e.g., a cleaning or a precoating performed after creating in a processing vessel the same atmosphere as in performing a process therein.
Conditioning times vary depending on the processing vessels. For instance, when process temperatures of the respective processing vessels are different from each other, the amount of time needed to raise the temperature to different process temperatures vary accordingly. Further, in case of performing different processes in the respective processing vessels, the cleaning times are different and, therefore, conditioning times are different. Moreover, since the cleaning times are determined based on the number of wafers to be loaded into the respective processing vessels in the aforementioned parallel processing, the cleaning times of the processing vessels are different from each other, making the conditioning times thereof different from each other.
In the conventional sequential processing as described above, the conditionings are started simultaneously in all processing vessels A to D, as shown in FIG. 8. Specifically, upon completion of conditioning SD of processing vessel D, which has the longest conditioning time S, the wafer is transferred to a first processing vessel A and then a processing PA is performed thereon. When a process P is completed in a preceding processing vessel, a transferring C of the wafer to a subsequent processing vessel is executed and a process P is performed therein.
As described above, by synchronizing the conditionings to start simultaneously in all processing vessels, there occur waiting time WA, WB, WC and WD between the time of completing the conditionings of the processing vessels and the time of starting the transferring of the wafers, which are different from each other.
For instance, though a process is first performed in the processing vessel A, the waiting time WA occurs until the conditioning time SD of the processing vessel D, which takes the longest time, lapses. Further, despite the long conditioning time SD of the processing vessel D and a processing PD thereof is performed last, there occurs a long wait time WD of the processing vessel D until the processes of the other processing vessels A to C are completed, since the conditioning thereof is started early.
As explained above, if there occur the different waiting time WA, WB, WC and WD in the processing vessels A to D, respectively, after finishing the conditionings thereof, an inner state of each processing vessel may undergo a subtle change before the wafer is loaded thereinto. In particular, the different waiting time period cause the temperature of each processing vessel (a temperature of a susceptor installed in each processing vessel or a temperature of each processing vessel affected by radiation of the susceptor) to be delicately changed, so that the temperatures of the processing vessels deviate from preset temperatures. Similarly in the above-described parallel processing, since the conditionings are simultaneously initiated in all processing vessels X, Y and Z, e.g., shown in FIG. 9, the different waiting time (WX=0), WY and WZ are generated. Thus, there is a problem with the processing results of the respective processing vessels, e.g., the thickness of films formed on a wafer delicately vary.
While sequentially processing a plurality of wafers, such a problem is most noticeable in a first processed wafer. The environment of each processing vessel is considered to be relatively more stable by the time of executing processing on the second wafer, compared to that during the processing of the first wafer. And during the processing of the first wafer, the environment is considered unstable.
Recently, a manufacturing of a semiconductor having a high accuracy is required with an advancement of a semiconductor product, which accompanies a demand for further improvement in accuracy in processing a semiconductor wafer, e.g., uniformity of a film formation or the like.